The present invention relates generally to a fuel delivery system for an internal combustion engine and, more particularly, to a fuel delivery system that employs two pressure regulators with a single electric fuel pump to deliver fuel to the engine.
Fuel injection systems are used to supply fuel to many modern engines because their ability to precisely meter fuel flow and accurately control the mixture of fuel and air delivered to an engine dramatically improves engine performance while reducing engine exhaust gas emissions. In one type of fuel injection system, a fuel pump transfers fuel under high pressure directly from a fuel tank to a fuel rail connected to the individual fuel injectors of the engine. Excess fuel not used by the fuel injectors during periods of low engine demand is returned to the fuel tank. Unfortunately, the returned fuel can vaporize or become aerated and foamy, which can lean out the air-fuel mixture delivered to the engine by the fuel pump.
As a result of recent passage of stringent emissions regulations and consumer demand for better performance, there is an increasing demand to employ fuel injection systems in two-stroke engines such as outboard marine engines. However, because the operating environment for outboard marine engines differs enormously from the operating environment for automobile engines, the design engineer faces considerable challenges not faced by the designer of automobile engines. For example, in order to prevent fuel from leaking from the fuel injection system and possibly igniting, U.S. Coast Guard regulations do not allow the use of a pressurized fuel line from a remote fuel tank to inboard engines. While outboards are typically exempt from the federal regulation, ABYC (American Boat and Yacht Council) standards which reflect the federal regulations, are generally applicable. U.S. Coast Guard regulations also prohibit the return of excess fuel from the fuel injectors to the fuel tank, as is typically done in automotive fuel injection systems. Hence, many fuel injection systems of the type commonly used in automobile engines are not usable in marine engines and some other two-stroke engines.
One proposed solution to the problem of injecting fuel in an engine without requiring the use of a pressurized external fuel line or a fuel return system requires dual fuel pumps for delivering fuel to the engine. A fuel delivery system 80 incorporating this proposed solution is schematically illustrated in FIG. 1. The fuel delivery system 80 includes first and second fuel pumps 88 and 92 that are located in a fuel supply line 84 and that are collectively configured to pump fuel from a fuel tank 82 to fuel injectors of the engine. In use, fuel is transferred first, under vacuum through the fuel supply line 84 from fuel tank 82 to fuel pump 88 through a primer bulb 86. (The primer bulb 86 is used only to prime the system with fuel before the start-up.) From the first fuel pump 88, fuel is transferred through the fuel supply line 84 to a vapor separator 90, where entrained vapor in the fuel is removed via a vent 98. Finally, the second fuel pump 92 transfers fuel from the vapor separator to all of the fuel injectors at a second, higher pressure than the first pressure generated by the first fuel pump 88. A pressure regulator 96 regulates the fuel pressure to the fuel injectors from the second fuel pump 92. Excess fuel from the second pump returns through the pressure regulator 96 to the vapor separator 90 through a fuel return line 94. The returned fuel is then available for use by the second fuel pump 92.
The pumping of excess fuel needlessly wastes power. Consequently, the first fuel pump 88 and the second fuel pump 92 run more often than necessary and use more power than is needed to supply an adequate amount of fuel at an adequate pressure under most engine operating condition. Also, the return of fuel to the vapor separator 90 carries engine heat to the fuel delivery system 80 that can increase the temperature and vapor pressure of the fuel in the fuel delivery system. The increased temperature and vapor pressure may cause fuel to flash into a vapor, leading to an effect commonly referred to as vapor lock. Vapor lock can result in erratic engine operation, loss of power output, or even cause the engine to stall or overheat.
Another major disadvantage of the fuel delivery system 80 illustrated in FIG. 1 is that it requires two fuel pumps 88 and 92. In some outboards, the first pump is a lift pump and is crankcase pulse driven while the second pump is electric. In others, both are electric. This can be problematic because electrical power demands on boats are rising due to a proliferation of electrically powered devices. These devices include convenience lights, headlights, compact disc players, and fish-locaters, as well as other electric power consuming devices and instruments. Every effort is being made to minimize the electrical power consumption of all outboard marine engine components in order to permit the use of a relatively small battery and/or alternator. These efforts may be frustrated if the engine""s electrical system must supply power to two separate electric pumps.
Another problem that may occur in certain types of internal combustion engines is an occasional inability to pump fuel, either from a fuel tank to a vapor separator or from the vapor separator to the combustion chambers of the engine. For instance, a fuel injected engine may continuously re-circulate portions of the fuel from the engine""s injectors back to the vapor separator. This continuous re-circulation of excess liquid fuel raises the temperature of the fuel and increases the likelihood that the fuel will reach a temperature at which it will vaporize within the fuel delivery system. If the fuel vaporizes to a gaseous state, certain types of pumps are unable to pump the vaporized fuel.
In view of the above-described potential problems relating to a fuel injected engine, the need therefore has arisen to provide a fuel delivery system that could remove excess liquid fuel from the fuel injectors and transfer the excess fuel back to the inlet of a single electric fuel pump of the engine without causing a vapor lock. It would be significantly beneficial if a fuel delivery system could be provided which does not require a separate low pressure fuel pump to transfer fuel from the fuel tank to the engine.
The invention relates to a fuel delivery system and method using two pressure regulators with a single electric fuel pump to deliver fuel to a fuel injector of an engine such as an outboard marine engine and to return excess fuel to the single electric fuel pump while avoiding vapor lock.
Accordingly, the present invention includes a single electric fuel pump that pumps fuel through a fuel supply line that connects a fuel tank to at least one fuel injector of the engine. A fuel return line connects the fuel injector to the single electric fuel pump via a vapor separator to remove excess liquid fuel from the fuel injector and to transfer the excess liquid fuel back to the single electric fuel pump for re-circulation. A first pressure regulator is disposed in the fuel return line upstream of the vapor separator to maintain a substantially constant pressure within the fuel injector while the vapor separator is purging entrained gas from the excess liquid fuel to prevent vapor lock. A second pressure regulator, located downstream of the vapor separator, allows the transfer of fuel to the single electric fuel pump from the vapor separator and also prevents reverse flow of fuel from the fuel tank to the vapor separator. This also serves to bias the pump inlet such that fuel is always drawn from the tank before being drawn from the separator. An engine control unit (ECU) receives a fuel pressure signal from a pressure sensor and transmits a fuel supply signal to the single electric fuel pump.
In accordance with another aspect of the invention, a method is provided for delivering fuel to at least one fuel injector of an engine. In accordance with this method, a single electric fuel pump draws fuel from the fuel tank via a fuel supply line and delivers the fuel to the fuel injector. Excess liquid fuel is removed from the fuel injector via a fuel return line and is transferred to the single electric fuel pump through a vapor separator for re-circulation. A first pressure regulator maintains a substantially constant pressure within the fuel injector while the vapor separator purges entrained gas from the excess liquid fuel. A second pressure regulator transfers excess liquid fuel back to the single electric fuel pump through the fuel return line while preventing reverse flow of fuel from the fuel tank to the vapor separator.
Various other features objects and advantages of the present invention will be made apparent from the following detailed description and the drawings.